OBJECTIONS TO THE THEORY OF MIMICRY 



107 



The next point insisted on was the paucity of recorded instances of attacks on butterflies 

 by insectivorous birds. Until recently this argument has not been without some justification. 

 There has, however, been recently communicated to the Entomological Society of London 

 an extremely valuable and interesting paper by Marshall, giving a collection of instances 

 in which birds have been observed to eat butterflies/ together with certain very potent 

 arguments on the subject which will be referred to later. 



Much stress was laid by Professor Packard on the explanation that resemblance between 

 butterflies is due to similarity of environment. This view, however, becomes untenable 

 when applied to resemblance between insects of different orders, and the environments 

 of which, in the early stages, the only ones which affect the ultimate pattern, are in many 

 cases very different. 



The only other important criticism which has come to the writer's notice is that con- 

 tained in the 'Cambridge Natural History'.^ The principal points here insisted upon are, 

 (i) that the phenomena are supposed to have occurred in the past, so that they cannot be 

 directly verified or disproved ; (2) that birds do not destroy butterflies in the perfect state ; 

 (3) that an amount of resemblance in the model that is assumed to be efficient at one step 

 of the development, and to bring safety, is at the next step supposed to be inefficient and 

 to involve destruction ; (4) that there is no sufficient evidence that the species which are 

 now similar were ever dissimilar. 



The first objection is not only a criticism of the special theory of mimicry, but amounts 

 to a complete repudiation of evolutionary theory in general. The upholders of the Bates- 

 Miiller theories maintain that natural selection is the governing force which has produced 

 and is producing mimetic phenomena, and probably no naturalist, least of all the distinguished 

 author of the section ' Insecta' in the 'Cambridge Natural History', would be prepared to 

 maintain that natural selection, if it ever affected butterflies in the past, has now ceased to 

 affect them. We cannot expect to see the process of selection actually and visibly taking 

 place, but we have remarkable evidence of the influence of the recent invasion of a foreign 

 species on the indigenous forms of Limenitis? It is therefore quite inconsistent with evolu- 

 tionary theory to suggest that mimetic resemblances are no longer in process of development . 



The evidence as to the attacks by birds is dealt with later at greater length. 



In reference to the third objection, it should be pointed out that the amount of 

 resemblance which first gives an advantage to its possessor is not assumed to bring safety, 

 but merely a slight advantage in the struggle, which advantage is liable to be increased 

 and perpetuated by further selection and more perfect resemblance. It is to be feared 

 that the inappropriate use of the word immune as applied to protected species is respon- 

 sible for many similar misconceptions as to the precise nature of the advantages which 

 dominant forms enjoy. It is not maintained that any species, however well protected, 

 is immune from one kind of attack or another. Real immunity in any species would bring 

 about such an increase in the number of individuals that the world would speedily become 

 uninhabitable for those creatures whose numbers remained at a normal figure. The con- 

 tention is rather that certain species are less destroyed by their natural enemies than are 

 others. A slight but recognizable modification in the appearance of a more palatable form 

 in the direction of one less palatable will convey to the former a comparatively better chance 

 of survival, but it does not bring immunity, and hence the modification remains capable of 



1 ' Birds as a Factor in the production of Mimetic 2 Insecta, Fart II, p. 337, et seq. 



Resemblances among Butterflies.' G. A. K. Marshall, ^ ' Mimetic North American Species of the Genus 



Trans. Ent. Soc, 1909, p. 329-83. Limenitis,' Poulton, Trans. Ent. Soc, 1907, p. 447-8. 



O 2 



